The present invention relates to an apparatus for gas sampling in capnography, more particularly to an airway adapter with a gas sampling line.
Capnography is the measurement of the level of carbon dioxide in the exhaled breath of a patient. This information is important in the diagnosis of a patient's pulmonary function. Usually measurements are continuous and carbon dioxide levels are displayed as a curve on a CRT display.
Capnographic measurements are performed by aspirating a continuous stream of gas from the patient's exhalation line which stream is fed through an aspirating line to an infra red sensor. The flow rate of the sample stream is usually 200 ml/min or less. In order to minimize dampening of the signal, the internal volume of the sampling line is kept as small as possible (about 2 ml.). The inside diameter of the sampling line is often 1 mm (0.040 inches) or smaller. The exhaled gases leave the patient at 99.degree. Fahrenhait and virtually 100 per cent relative humidity. Some condensation occurs in the in-line connector and additionally in the sampling line as the gas continues to cool to room temperature (usually around 70.degree. F.). The small diameter of the sampling line is very susceptible to clogging by mucus expectorated by the patient and the liquid condensate.
There are several prior art combination airway adapter and sampling tube products available in the market place made or sold by companies such as Engstrom, Allegheny, Novametrix, Biochem, Gould, Puritan-Bennett, Carburos-Melabicos, Datex, Godart, Ohmeda, Traverse Medical, Sensormedics and Siemens-Elena. Typically, the product includes an in-line connector, i.e. a connector, usually plastic, which fits within the exhalation tube of the patient, and a sampling tube coupled between the connector and the sensing instrument. The connector is usually of T-configuration or an elbow. The sampling line is usually nylon or Nafion or vinyl and may or may not be equipped with fittings such as luer fittings at one or both ends. Sometimes a filter and/or water trap is provided usually between the sampling line and the instrument. Some systems are equipped with means to reverse the gas flow to clear a clog.
In the Datex made product, sold by Puritan-Bennett and Carburos-Melabicos, the in-line connector is a molded fitting with an integrally bonded tube that extends inside by about a quater inch. The Ohmeda product comprises an in-line connector which is an elbow fitting with a sampling line extending inside for about 3/8 of an inch. The line appears to be pressed into the elbow approximately coaxially aligned with one of the legs of the elbow.